The evolution of the richness of content broadcast by the Internet combined with an ever increasing quality of experience of users, notably in terms of instantaneity, whether this refers to the consultation of content on line or to games played by players who are far away form each other, is leading content providers and network operators to locate content remotely and to duplicate it as close as possible to users, when that makes sense.
The expansion of the Internet has led in recent years to an explosion in traffic in terms of the richness of the data transported, essentially because the streams concerned are mass market video programs, for example Netflix, Youtube, etc. The transit networks (intercontinental fibres, national networks), the backhauling networks and the access or “local loop” networks are saturated. This causes loss of packets by the routers and the necessity to retransmit the corresponding programs (television programs or video) as well as the other streams that are also impacted as a consequence and in an undifferentiated manner. The increase in the transfer time caused by these retransmissions, because of the reduced performance of the networks, leads to a deterioration of the quality as perceived by users.
To attempt to solve these problems, network operators have deployed infrastructures offering better performance in terms of data rate and making it possible to transport high volumes, but this is an endless race between increasing the capacity of the networks and the increasing richness of the content in transit over the same networks; hardly have new infrastructures been deployed than new content encoding standards become available (SDTV, HDTV, 4K, 8K, etc.).
An alternative approach has therefore been proposed by Internet players using telecommunication networks in order to offer an improved quality of experience (QoE) to end users (content access delay, content richness): dedicated storage, management, content access and user request management architectures known as content delivery network (CDN) architectures, by duplication of the content in “caches” located as near users as possible, make it possible to reduce contention in the transit networks and therefore to reduce the delay in accessing that content.
These CDN have been installed in terrestrial networks and in the infrastructure networks of telecommunication operators.
Broadband terrestrial infrastructures cannot reach all subscribers, however, notably for economic reasons, the cost of deployment of optical fibres, ADSL copper networks or fourth generation (4G) or fifth generation (5G) terrestrial wireless networks potentially becoming unacceptable if the subscriber density falls too low.
Some players have therefore proposed in the past or more recently the deployment of constellations of satellites in non-geostationary orbit (NGSO) i.e. in low Earth orbit at between 500 and 2000 km altitude and in medium Earth orbit at between 6000 and 20 000 km altitude. This type of solution offers a propagation delay compatible with those encountered in terrestrial networks, i.e. a few tens of milliseconds (ms) for the lowest orbits. On the other hand, the deployment of such a constellation requires use of several tens of satellites (e.g. in the O3bNetworks, Globalstar or Iridium, Skybridge satellite networks) to several hundred satellites (e.g. Teledesic or WorldVu) in order to guarantee continuity of service in the inhabited areas of the terrestrial globe. Moreover, a satellite in low earth orbit offers a limited capacity compared to a geostationary satellite in a comparable point to point configuration, but makes it possible to limit the cost of the space infrastructure by launching a plurality of satellites on each launch vehicle. Because of their altitude and low latency, this type of satellite contributes to an efficient use of the telecommunication network, with performance comparable to that of terrestrial networks.
Geostationary Earth Orbit (GEO) satellites (orbiting at a distance of 35 786 km in the equatorial plane of the Earth), for their part, have the advantage of covering a large area of the surface of the Earth (up to ⅓ of that surface); the same content can therefore be received simultaneously by several hundred thousand users, even millions of users, thereby reducing the cost of transmission of the same content in the same proportion. However, the transmission delay of a geostationary satellite (more than 500 ms between two points on the Earth for a round trip) is very much greater than the delays encountered in terrestrial networks and incompatible with real time use and with the quality of experience now encountered in terrestrial networks (a few tens of milliseconds), when the content must be downloaded via a geostationary network of this kind in an interactive context (for example when consulting a Web page via a browser). Moreover, in order to circumvent this obstacle, dedicated protocols or devices (for example the Performance Enhancement Proxy (PEP) protocol) must be used by the satellite network operators in order to integrate their solutions into terrestrial networks, often to the detriment of security.
US patent 2002/0031102 describes a system using the DSN service to enable a user to access the Internet. D1 uses a dynamic cache to store the most requested IP addresses.
The patent application WO 2010081160 describes a system and a method making it possible to optimize communication performance in a WEB context.
In this document, the term “CDN” designates a set of servers connected in a network that cooperate to make content or data available to users via caches, a microcache is a cache situated at the level of a geostationary or non-geostationary satellite network, a nanocache is a cache situated at a user access point closest to a user (at the level of the user terminal of the satellite network itself, serving a local loop to which a set of users are connected—as in a village or a small business, for example—or serving a single user—as in a home, for example). The term “cache” is well known to the person skilled in the art and is not explained further here.
The expression “end user” refers to a user accessing a data content or transferring data to the network to exchange of data with other users via a terminal intended to interact with a telecommunication network, terrestrial or otherwise.
The introductory description indicates that the altitude criterion is essential for delivering a service enabling a network with non-terrestrial infrastructures to be integrated into terrestrial networks, the propagation delay being crucial. Types of platform other than non-geostationary satellites meet this criterion: drones (non-piloted aircraft) and stratosphere balloons (stabilized balloons). Hereinafter, the expression “vehicle in low Earth orbit” therefore refers to a non-geostationary satellite, a stratosphere balloon, a drone, for example. In the remainder of the patent the NGSO terminology therefore embraces the expression “vehicle in low Earth orbit”.
An NGSO network is a telecommunication network made up of terrestrial user stations, terrestrial access stations connected to the telecommunication infrastructures and to a set of NGSO vehicles. Terrestrial user stations are interconnected to the access stations via NGSO vehicles.